Penetrometers and related devices have been used for a variety of geotechnical engineering purposes over the years. Among the well-known types of penetrometers is the utility dynamic cone penetrometer (“DCP”) which is commonly used by utility companies to determine the adequacy and degree of soil compaction in restorations of openings made in roadways or other land features for the purpose of installing or maintaining underground facilities. Other types of DCPs are also presently known to be used in evaluating parameters in addition to soil compaction, including for example resistance to penetration or shear strength.
Generally, DCPs consist of an elongated shaft having a first and second flange spaced a standardized distance apart with a standardized drop weight conveyed freely there-between on the shaft. The DCP further has a conically shaped tip that is driven into the soil by means of the drop weight being lifted to the height of the first flange and then dropped onto the anvil, or second flange, attached to the shaft. Typically, the drop weight of most DCPs has a standardized mass and a standardized range of movement along the shaft, and thus the driving energy caused by the drop weight striking the anvil is also standardized. In common usage, the operator of the DCP will position the tip of the penetrometer on a soil to be evaluated and with one hand will raise the weight up to the first flange, which is located below a handle provided for steadying the device with the other hand. The weight is then released and permitted to fall freely by gravity. The driving energy generated by the weight hitting the anvil causes the tip of the DCP to move in a downward direction into the soil. Generally, the process of raising and releasing the weight to strike the anvil will be repeated until a standard depth of penetration is established. At that time a record is made of the number of times the anvil has been raised and dropped, as an indication of the relative compactness of the soil. If the required blowcount is reached before the standard penetration is reached, this automatically means a passing condition, and further blows are unnecessary, and not usually pursued.
The utility DCP is usually used in a go/no-go fashion, in which the number of blows by the drop weight to the anvil to achieve a standard depth of penetration is compared with a predetermined standard: if the number of blows equals or exceeds the standard, the compaction of the soil is deemed adequate. If the number of blows, however, does not meet or exceed the predetermined standard, additional compaction of the soil is performed until the standard is met. Certain soils may require a different criterion; one such is poorly-graded sand, for which the blow-count is determined for a greater depth of penetration, and thus one or more additional gradation lines can be provided on the shaft near the tip to assist in determining appropriate compaction.
DCPs are generally manual testing devices, relying exclusively on the ability of the user to record test results. Automation approaches by others in the field of soil testing, involve the use of some electronic measuring assemblies attached to the DCP. One such implementation involves a linear variable differential transformer sensor (e.g., an LVDT sensor) that extends from the DCP to the soil. Another implementation, by Applied Research Associates, Inc. (“ARA”) (marketed by Vertek as a Data Acquisition System (“DAS”)), features a portable DAS that utilizes a string potentiometer attached to a hook on the DCP rod anvil in such a way as to monitor the DCP penetration. These presently known automated approaches however are generally cumbersome and fragile and further lack the ability to readily transmit data collected by the DCP to remote data-logging and display devices, such as portable computers or personal digital assistants (“PDAs”) for secure logging and retention of data. Existing automated approaches are also generally unable to effectively display the collected data in real-time or transmit the data by means of wireless transmitters.
Accordingly, there is a need for an automated device and method to relieve a user of a DCP from the arduous task of keeping track of data manually. It would thus be advantageous to have a device to alleviate the need for the user to manually measure the distance that the DCP has moved during a particular evaluation, and further that would free the user from having to manually count the number of times that the drop weight strikes the anvil. It would additionally be advantageous if such an innovation could determine whether the drop weight of the DCP has been raised to an appropriate position before being released in order to generate the standardized driving force. Such an innovation would ensure that the evaluation being carried out by the DCP is proper and would alert the user when certain drops of the weight were invalid and require repetition of the test. Use of such an automated device and method in connection with a DCP would lessen the likelihood of user error and thus provide a more accurate and reliable assessment of the compaction of soil being evaluated. An automated device and method of collecting data generated by a DCP would further provide a more permanent, secure and tamper-proof record for test data, including, but not limited to, data concerning site location, soil description, lift thickness, and blowcount and depth of penetration patterns.
Another difficulty in determining soil compaction (and/or other soil properties) is posed by the smaller openings, such as keyhole openings, that have begun to be used by utility companies, and others, in operations that require installation or repair of underground equipment or settings. Keyhole openings are typically smaller than 18-inches in diameter (when circular) or on a side (when rectangular). These openings have become feasible due to the development of tools allowing work to be performed on underground facilities from the surface through tight or enclosed spaces. As operators cannot physically enter such openings, compaction and verification of soil at the bottom of the opening must be performed from the surface above and outside of the so called “keyhole”. The DCPs of the prior art as presently configured cannot be used for this purpose as readings are almost impossible to be made with any accuracy due to the limited sight lines available.
Accordingly, it would also be desirable to have a device and method to enable use of a DCP in a keyhole or in other applications in which a DCP is to be used to evaluate soil at the bottom of a small opening. It would be further advantageous for such a device and method to be automated in order to simplify the collection, recordation, monitoring and transmission of compaction data generated by the DCP so that it can be evaluated in real-time by the user and others from a remote location, and so that the data can be transferred to and stored at a centralized database for comprehensive record keeping, or transmission to others for analysis.